Ryan Houdek
f9b352a093
When a fork occurs FEX needs to be incredibly careful as any thread
(that isn't forking) that holds a lock will vanish when the fork occurs.
At this point if the newly forked process tries to use these mutexes
then the process hangs indefinitely.
The three major mutexes that need to be held during a fork:
- Code Invalidation mutex
- This is the highest priority and causes us to hang frequently.
- This is highly likely to occur when one thread is loading shared
libraries and another thread is forking.
- Happens frequently with Wine and steam.
- VMA tracking mutex
- This one happens when one thread is allocating memory while a fork
occurs.
- This closely relates to the code invalidation mutex, just happens at
the syscall layer instead of the FEXCore layer.
- Happens as frequently as the code invalidation mutex.
- Allocation mutex
- This mutex is used for FEX's 64-bit Allocator, this happens when FEX
is allocating memory on one thread and a fork occurs.
- Fairly infrequent because jemalloc doesn't allocate VMA regions that
often.
While this likely doesn't hit all of the FEX mutexes, this hits the ones
that are burning fires and are happening frequently.
- FEXCore: Adds forkable mutex/locks
Necessary since we have a few locations in FEX that need to be locked
before and after a fork.
When a fork occurs the locks must be locked prior to the fork. Then
afterwards they either need to unlock or be set to default
initialization state.
- Parent
- Does an unlock
- Child
- Sets the lock to default initialization state
- This is because it pthreads does TID based ownership checking on
unique locks and refcount based waiting for shared locks.
- No way to "unlock" after fork in this case other than default
initializing.
FEX - Fast x86 emulation frontend
FEX allows you to run x86 and x86-64 binaries on an AArch64 host, similar to qemu-user and box86. It has native support for a rootfs overlay, so you don't need to chroot, as well as some thunklibs so it can forward things like GL to the host. FEX presents a Linux 5.0 interface to the guest, and supports both AArch64 and x86-64 as hosts. FEX is very much work in progress, so expect things to change.
Quick start guide
For Ubuntu 20.04, 21.04, 21.10, 22.04
Execute the following command in the terminal to install FEX through a PPA.
curl --silent https://raw.githubusercontent.com/FEX-Emu/FEX/main/Scripts/InstallFEX.py --output /tmp/InstallFEX.py && python3 /tmp/InstallFEX.py && rm /tmp/InstallFEX.py
This command will walk you through installing FEX through a PPA, and downloading a RootFS for use with FEX.
Ubuntu PPA is updated with our monthly releases.
For everyone else
Please see Building FEX.
Getting Started
FEX has been tested to build and run on ARMv8.0, ARMv8.1+, and x86-64(AVX or newer) hardware. ARMv7 and older x86 hardware will not work. Expected operating system usage is Linux. FEX has been tested with Ubuntu 20.04, 20.10, and 21.04. Also Arch Linux.
On AArch64 hosts the user MUST have an x86-64 RootFS Creating a RootFS.
Navigating the Source
See the Source Outline for more information.
Building FEX
Follow the guide on the official FEX-Emu Wiki here.
RootFS generation
AArch64 hosts require a rootfs for running applications. Follow the guide on the wiki page for seeing how to set up the rootfs from scratch https://wiki.fex-emu.com/index.php/Development:Setting_up_RootFS
